Open-loop fluidic analog accelerometer



1970 R. A. KANTOLA ETAL ,540, 58

OPEN-LOCI FLUIDIC ANALOG ACCELEROMETER Filed May 29, 196'? 2Sheets-Sheet z I Al},

Z PASS 2 7% 2717157? [27 van t; ans: Robert A. Kanbo/a, l4 f///'.s A.Boothe,

y q Q 5m US. Cl. 73-71 4 Claims ABSTRACT OF THE DISCLOSURE Apparatus forsensing acceleration or vibration and generating an analog-typepressurized fluid signal proportional to the magnitude of the associatedevent. Linear acceleration or vibration is sensed by a flexure-mountedinertial mass including a hollow, elongated spring member of thecantilever beam type having a first end rigidly fixed in position and asecond unsupported end upon which the acceleration-sensitive inertialmass is mounted. The hollow portion of the spring member issues a fluidjet from the second unsupported end directed at fluid receivers, theflexure of the spring member causing distribution of the jet between thereceivers in proportion to the magnitude of the acceleration. Angularmotion acceleration is sensed by utilizing a cylindrical inertial massconnected along its longitudinal axis to two torsional spring membersrigidly fixed in position at their far ends such that the cylindricalmass is subject to rotation in the presence of an angular motionacceleration.

CROSS-REFERENCE DATA TO RELATED APPLICATION A concurrently filed US.patent application, Ser. No. 642,115, inventors l. N. Shinn and C. G.Ringwall, entitled Closed-Loop Fluidic Analog Accelerometer is assignedto the same assignee as the present invention and discloses and claims aclosed-loop embodiment of the subject open-loop fluidic analogaccelerometer.

Our invention relates to a fluidic type of accelerometer providing ananalog output, and in particular, to a friction-free, open-loop, fluidicaccelerometer having a flexure-mounted means for sensing linear orangular motion acceleration to thereby provide a highly reliableaccelerometer.

Accelerometers are devices for sensing the magnitude of particularacceleration events and find typpical application in guidance andnavigation systems for high performance aircraft in which their outputis applied to other mechanisms for further computational or controlfunctions, or for direct reading of the acceleration event. Prior artaccelerometers are relatively complex structures having several movingparts subject to sliding motion and resultant frictional wear or othertype of frictional motion which inherently causes degradation of theperformance or actual failure of the accelerometer. The recentlydeveloped fluidics field employing no-moving parts devices known asfluid amplifiers otters promise of improved types of accelerometershaving simplified structure and substantially unlimited lifetime. Aprior art fluidic accelerometer employs as liding piston supported by anair bearing in a cylinder filled with a suitable fluid for sensingacceleration by the motion of the piston responsive to the accelerationevent, and fluid amplifier circuitry for merely amplifyfing the fluidsignals picked off from the piston-cylinder arrangement. Although theair bearing reduces friction, it requires high precision, close-fittingparts which inherently are susceptible to contamination and warpage.Thus, the advantages of fluid amplifiers in their capability ofwithstanding extreme United States Patent 3,540,268 Patented Nov. 17,1970 environmental conditions such as shock, vibration, nuclearradiation and high temperature and their no-moving parts feature whichpermits substantially unlimited lifetime cannot be utilized with thisprior arm accelerometer since the acceleration-sensing element failslong hefore any possible failure of the fluid amplifier circuitryassociated therewith.

Therefore, one of the principal objects of our invention is to provide anew fluidic analog-type accelerometer having a friction-freeacceleration sensing portion constructed of parts not requiring highprecision to thereby utilize the full advantage of fluid amplifiersassociated therewith.

Another object of our invention is to provide the accelerometer forsensing one-axis or two-axes linear motion acceleration.

A further object of our invention is to provide such accelerometer forsensing angular motion acceleration.

A still further object of our invention is to provide an open-loopfluidic accelerometer.

Briefly summarized, our invntion is a new open-loop fluidic analogtypeaccelerometer. The sensor element of the accelerometer is comprised of aspring-mass device in the form of a flexure-mounted inertial massresponsive to the acceleration event which may be of the linear orangular motion type. In the case of the linear motion accelerometer, thespring-mass device comprises a hollow, elongated spring member of thecantilever beam type having a first end rigidly fixed in position aboutwhich the spring member flexure occurs, and a second unsupported endupon which the acceleration-sensitive inertial mass is mounted andrigidly attached thereto. The hollow portion of the spring member servesas a fluid passage wherein the fixed end thereof is supplied with apressurized fluid and a fluid jet issues from the mass-mounted end. Apair of spaced fluid receivers are positioned coplanar with a selectedaxis along which the spring member is constrained to flex such that thefluid jet issuing therefrom is directed midway between the receivers inthe nonflexed state of the spring member and is distributed between thereceivers in a proportion varying with the magnitude of the accelerationevent along the selected axis. The analog fluid signal developed by thedifferentially pressurized fluid recovered in the two receivers may besupplied to the fluid amplifier circuitry for generating a signal ofsuflicient pressure level for further utilization thereof in a system inwhich the accelerometer is a component. One-axis linear motionacceleration is sensed by construction of the spring member forstiffness in a lateral direction such that the only flexure is coplanarwith the selected axis determined by the position of the fluidreceivers. Two-axis linear motion acceleration is sensed by providing asecond pair of fluid receivers positioned coplanar with a secondselected axis generally perpendicular to the first axis associated withthe first pair of receivers. The angular motion accelerometer embodimentof our invention comprises a cylindrical acceleration-sensitive massattached along its longitudinal axis to two torsional spring membersrigidly fixed in position at their far ends such that the cylindricalmass is subject to rotation in the presence of an angular accelerationevent. A fluid jet in communication with the cylindrical mass is sensedby two receivers for developing a differentially pressurized analogfluid signal representing the magnitude of the angular motionacceleration event in a manner similar to that of the one-axis linearmotion acceleration sensor.

The features of our invention which we desire to protect herein arepointed out with particularity in the appended claims. The inventionitself, however, both as to its organization and method of operation,together with further objects and advantages thereof, may best beunderstood by reference to the following description taken in connectionwith the accompanying drawings wherein like parts in each of the severalfigures are identified by the same reference character, and wherein:

FIGS. la and 1b are respective views, partly in section, of twoembodiments of the acceleration-sensitive portion of a one-axis linearmotion accelerometer constructed in accordance with our invention;

FIG. 2 is a schematic diagram of the one-axis linear motionaccelerometer partially illustrated in FIG. 1;

FIG. 3a is a two-axis embodiment of the linear motion accelerometer ofFIGS. 1 and 2 and further illustrates;

FIGS. 3b and 3c are enlarged views of two other types of fluid receiversthat may be employed; and

FIGS. 4a and 4b illustrate two embodiments of the acceleration-sensitiveportion of an angular motion accelerometer constructed in accordancewith our invention.

Referring now to the drawings, in FIG. 1a there is shown, partly insection, a one-axis linear motion acceleration sensor comprising thespring-mass and receiver portion of our linear motion fluidic analogaccelerometer. The spring-mass device is in the form of aflexure-mounted inertial mass comprising a resiliently flexible,elongated body 11 of the cantilever beam type having a first end 12thereof rigidly fixed in position and a second unsupported end 13 uponwhich a body comprising an acceleration-sensitive (inertial) mass 16 ismounted and rigidly attached thereto. Bodies 11 and 16 may be distinctor one integral body. Body 11, hereinafter also described as a springmember, is provided with a hollow center portion running longitudinallyof the spring member to form a fluid passage 14 therethrough. Body 16may have any of a number of forms, but preferably is symmetrical aboutthe plane of motion. A first end 14a of the fluid passage is adapted forconnection by any suitable means to a source of fluid P pressurizedabove ambient, and which may be a liquid or gas including air. Thesecond end 15 of fluid passage 14 is the form of a fluid flow restrictoror nozzle for generating a jet of the pressurized fluid which issues ina straight path aligned with the longitudinal axis of passage 14 in theregion of the second end 115 thereof. Mass 16 is positioned in a planeperpendicular to the axis of fluid passage 14 when spring member 11 isin its nonflexed state and may be positioned in proximity with thesecond end 13 thereof, as illustrated, or at the very extreme end andintegral therewith. For the case of the one-axis linear motionacceleration sensor, spring member 11 further includes a fin structure17 integral with the hollow member 14 and mass 16, and is also rigidlyfixed in position at the supported end 12 to provide stifiness in thelateral direction such that spring member 11 is constrained to beresiliently flexible as a cantilever beam along only a single axisperpendicular to the plane including fin member 17 in the nonflexedstate of spring member 11. It is appreciated that the unsupported end 13of member 11, and thus also mass 16, are constrained to move in a pathwhich is a segment of an are at whose null point the tangent to the pathis in the direction along the axis in which acceleration is to besensed, however, the degree of movement of unsupported end 13 and mass16 is relatively small and spring member -11 is of elongated form suchthat as a good approximation the movement can be considered to be linearalong the sensitive axis.

A housing for supporting the spring-mass device is a structurally rigidopen frame 18 rigidly fixed in positron, such as by attachment to anaircraft structure subect to the external acceleration event beingsensed, and oriented preferably such that the nonflexed state of springmember 11 is perpendicular to the axis of the singleaxis linear motionacceleration event being sensed. Thus, in the illustration of FIG. 1a,frame 18 is positioned such that spring member 11 in the nonflexed stateis oriented perpendicular with respect to the linear motion accelerationaxis indicated by arrows 19. Member 11 is resiliently flexible about thesupported end 12 in response to the linear acceleration event 19 whereinresiliently flexible is defined as the characteristic of member 11flexing in the manner of a loaded cantilever beam in response to theacceleration event and returning tov its nonflexed state in a subsequentabsence of the acceleration. Frame 18 includes a second portion 20 forcontaining two spaced fluid receivers 21 and 22 positioned coplanar withthe selected axis 19 downstream of nozzle 15 such that in the nonflexedstate of member 11 the fluid jet issuing from nozzle 15 is directedmidway between the two receivers to thereby provide equal pressurizedfluid signals in two fluid passages 23 and 24 which are connected to theoutputs of receivers 21 and 22, respectively. The distance between thenozzle end 15 and downstream receivers 21, 22 determines the sensitivity(gain) of the acceleration sensor and such distance may be in the rangeof 1 to 20 times the smallest nozzle exit dimension. Within this rangeof spacings, the fluid jet is assumed to have minimum divergence in itspath from the nozzle to the receivers, and the sensitivity increaseswith decreased noZzle-to-receiver spacing. Thus, in the absence of anacceleration event having at least a component along axis 19, thedifferentially pressurized fluid signal developed between passages 23and 24 by the fluid pressure recovered in the receivers is zero.Passages 23, 24 and all the other fluid passages interconnectingelements of our accelerometer are of circular cross section, or othershapes as desired, constructed of a material compatible with the fluidmedium employed. It is noted that none of the elements of ouraccelerometer are constructed as high precision parts.

Now assume that a linear motion acceleration event or component thereofdevelops along the indicated axis 19. Under this condition ofacceleration which is as sumed a linear motion acceleration, although itis recognized that a tangential component of angular motion accelerationcan also be sensed, spring member 11 flexes in the manner of a loadedcantilever beam, and in particular, the unsupported end 13 of member 11flexes due to the mass-acceleration force F=ma being developed by mass(m) 16 accelerating along axis 19 in the same direction as frame 18accelerates but in an opposing direction relative to the null pointmidway between the receivers. This mass-acceleration force is opposed bythe resiliency(spring rate)force of member 11 tending to return mass 16to its null (zero acceleration) position, and the steady-state positionof mass 16 is determined by a balance of these forces. The magnitude ofthe displacement of end 13 (and mass 16) from its nonflexed (null)position is directly proportional in a linear relationship to themagnitude of the acceleration event along axis 19. In the event of aconstant acceleration event, member 11 attains the state of flexureproportional to the magnitude of the acceleration and remains in suchstate for the duration of the constant acceleration. The motion of mass16 from its null position to a steady-state position displaced from thenull corresponding to a constant acceleration event may be somewhatoscillatory or without any overshoot depending upon the mechanicaldamping provided in the spring-mass device. A mechanical damping factorin the range of 0.20 to 0.70 for the structure illustrated in FIG. 1a ispreferably employed in our open-loop accelerometer. The mass of hollowmember 14 and fin member 17 is made as small as possible, such that theprimary acceleration-sensitive body, mass 16, has a mass greater thanthe total mass of members 14 and 17 by a ratio of at least 5:1. Althoughthe cross section of the fluid passage within hollow member 14 isillustrated as being circular,it may be of other shapes such asrectangular or elliptical, and, as illustrated in FIG. 1b, theelliptical cross section of hollow member 14 may be sufliciently stifflaterally to omit the need for pro viding fin members 17 as in the caseof the FIG. la embodiment. In addition, the circular shaped receiversindicated in FIG. la may also have other shapes such as the rectangularillustrated in enlarged nozzle-receiver FIG. 1b. A center vent passage25 may also be provided, if desired, intermediate receivers 21 and 22.

A specific example of the dimensions of our one-axis linear motionaccelerometer sensor having as the spring member 11 a hollow reed ofrectangular cross section, and constructed of 0.005 inch steel follows:The reed is 2 inches long having outside dimensions of 0.030 inch(height) by 0.210 inch (width). The nozzle-to-receiver spacing is 0.200inch, equal to ten times the reed inside height dimension. The receiverseach have a height dimension equal to the inside height dimension of thereed, and are spaced apart by a center vent as illustrated in FIG. 1b,having a dimension equal to one-half a receiver height dimension. Theweight of mass 16 is approximately 0.03 pound and the mass of the reedalone is approximately 5% of this amout. The deflection of the jet atthe receivers for this specific sensor is 0.00905 inch per gravitationalunit of acceleration (inch/ G) wherein G=32.2 feet/second, and theoutput differential pressure change per unit of deflection varieslinearly with supply pressure for incompressible flow and is 16.5p.s.i.d./ inch/p.s.i. wherein p.s.i.d. is pounds per square inchdifferential. Thus, the sensor sensitivity is 0.281 p.s.i.d./G/ p.s.i.,and can be readily increased by increasing supply pressure P withinlimits.

Our open-loop fluidic accelerometer is a satisfactory device for sensingacceleration but the flexure of spring member 11 and attendant movementof mass 16 may become relatively large for acceleration events havingexceptionally large magnitudes, resulting in a nonlinear relationshipbetween the position of mass 16 from null and the differential pressuresignal developed in response thereto. The degree of mass 16 movementmay, of course, be decreased by decreasing the weight of mass 16 orincreasing the stiffness of member 11 along axis 19 at some expense insensor sensitivity.

Our open-loop accelerometer is illustrated schematically in FIG. 2. Afluidic low pass filter 26 comprising a serially connected fluidresistor R and capacitor C effectively removes any high frequencycomponents in the analog signal in each of passages 23, 24 due to theprobably underdamped response of the flexure-mounted mass 16 in the caseof compressible fluids. For incompressible fluids an inductor-resistorcircuit is used as the filter. One or more stages of analog-type fluidamplifiers 27 are also preferably employed for amplifying the filteredsignal to a level AP for further utilization thereof.

The single-axis fluidic accelerometer illustrated in FIGS. 1 and 2 maybe converted to a two-axis linear motion accelerometer as illustrated inFIG. 3a in the following manner. The fin portion 17 for rendering springmember 11 stiff in the lateral direction is omitted and a resilientlyflexible tube 14 preferably having a circular cross section is utilizedas the spring member. The first and 12 of tube 14 is rigidly supportedwithin portion 18 of the frame housing in its passage through the wallthereof such that tube is equally resiliently flexible in alldirections. A second pair of spaced receivers 30 and 31 are positionedcoplanar with a second selected axis herein designated x which forpurposes of exemplification is perpendicular to the first axis 19 hereindesignated y along which the first pair of receivers 21 and 22 arepositioned. The two pairs of receivers 21, 22 and 30, 31 are eachequally spaced and define the two axes x, y along which an externalacceleration event is to be sensed. The four receivers are oriented suchthat in the nonflexed (null) state of spring member 14, the fluid jetissuing from nozzle is directed centrally of the arrangement of fourdownstream receivers and distributed equally thereamong, or vented to acentral vent (not shown), to provide equal pressurized fluid signals inthe four passages 23, 24, 32, 33 connected to the outputs of thereceivers. Thus, in the absence of an acceleration event having at leasta component within the x-y plane, the x and y-axis differentialpressurized fluid signals developed between passages 3233 and 23-24,respectively, are zero..A fluidic circuit 26, 27 which may be of thesame type illustrated in FIG. 2 providing high frequency filtering andamplifying characteristics is connected to fluid passages 23 and 24 toprovide a differentially pressurized y-axis output fluid signal AP Inlike manner, fluid passages 32 and 33 are connected to a second fluidiccircuit 34, 35 identical to circuit 26, 27 to develop at the outputthereof a differentially pressurized x-axis output fluid signal APAlthough the fluid receivers 21, 22, 30, and 31 in FIG. 3a areillustrated as being of circular shape, they may also have the shapeillustrated in FIG. 3b, a sector of a ring, the advantage of this shapebeing that a lower output fluid impedance is obtained for suppylinggreater output flow since the receivers intercept a greater portion ofthe fluid jet. A third arrangement of fluid receivers is illustrated inFIG. 30 comprising a cruciform arrangement of twelve receivers. Thetwelve receivers are in four groups, each comprising three receiversinterconnected at their outputs for supplying the four fluid passagesleading to the two fluidic filter circuits '26, .34. The interconnectedreceivers in each group are indicated by the numerals designating thefour receivers in FIGS. 3a and 3b. Center vents 25 can be used with eachof the receiver arrangements illustrated in FIGS. 3b and 30, if desired.

Fluid alalog accelerometers for sensing angular motion acceleration andbeing friction-free in operation and constructed of parts not requiringhigh precision are illustrated in FIGS. 4a and 4b. In both of FIGS. 4aand 4b, as in the case of the linear motion accelerometer, theacceleration-sensitive portion of the accelerometer comprises aflexure-mounted inertial mass. In the case of our angular motionaccelerometer, the inertial mass is a cylindrical body 16 of mass mrigidly attached to and supported along its longitudinal axis by thenear ends of two aligned torsionally resilient members 40 and 41 havingtheir far ends rigidly fixed in position to frame member 18. Torsionallyresilient members 40 and 41 may comprise tubes of the type 14illustrated in FIG. 3a, preferably proportioned for greater stiffness inbending than in torsion. Mass 16 thus undergoes a resiliently rotationalmotion about its axis in response to an angular motion accelerationevent 19 which occurs about such axis in a plane perpendicular orsubstantially perpendicular thereto.

Referring now in particular to FIG. 4a, mass 16 is provided with ahollow center portion 42 which forms a fluid passage preferably circularin cross section, although other shapes may also be utilized, extendingalong the longitudinal axis of mass 16 from the bottom end thereof toapproximately the center and thence extending radially outward andterminating in a nozzle shape 15. A pair of spaced fluid receivers 21and 22 are positioned in the plane of rotation of mass 16 and orientedsuch that in the null position of mass 16, wherein members 40 and 41 arein their torsionally nonflexed state, a fluid jet issuing from nozzle 15is directed midway between the downstream two receivers to therebyprovide equal pressurized fluid signals in two fluid passages 23 and 24connected with the outputs of receivers 21 and 22, respectively.Torsionally resilient member 41, being hollow, also provides a fluidpassage interconnecting passage 42 to a source of pressurized fluid Ppassage 41 illustrated as being coupled in fluid-tight relationship withpassage 42 in region 44. The differentially pressurized fluid signalbetween passages 23 and 24 is supplied to the input of a fluidic circuit26 which may be of the same type as illustrated in FIG. 2 to filter outany high frequency components, and one or more stages of analog fluidamplification 27 may also be utilized. The operation of our angularmotion accelerometer may be described as follows: Under conditions ofzero angular motion acceleration, the pressures recovered in receivers21 and 22 are equal such that the differentially pressurized fluidsignal developed between passages 23 and 24, and the output differentialpressure signal AP are both zero. Under conditions of an angular motionacceleration of frame 18 along path 19, the acceleration torque due tomass 16 being subjected to rotational acceleration causes torsionalspring members 40, 41 to be flexed by twisting in the same direction asframe 18 accelerates but in an opposing direction relative to the nullpoint midway between the receivers. The flexure of members 40, 41 andrelative rotationof mass 16 is of magnitude directly proportional in alinear relationship to the magnitude of the angular acceleration alongpath 19. Counteracting the acceleration torque is the resiliency torqueof members 40, 41 tending to return mass 16 to its null position. Abalance of the acceleration torque and resiliency torque determines thesteady-state angular position of mass 16 for constant acceleration.

Referring now to FIGURE 4b, there is shown a second embodiment of theangular acceleration sensing portion of the angular motion accelerometerillustrated in FIG- URE 4a. The distinction between the two embodimentsis the means for supplying the differentially pressurized fluid signalto the input of passages 23 and 24 which are connected to the input offluid circuit 26. In the FIG. 4b embodiment, torsionally resilientmember 41 does not provide the additional function of a fluid passage asin the case of the FIG. 4a embodiment, nor is there any need for ahollow portion within mass 16.

In the FIG. 4b embodiment, a pair of fluid passages 50 and 51 suppliedfrom a source of pressurized fluid P each include a fluid flowrestrictor 53 and terminate in aligned nozzles 54 and 55, respectively,positioned within the plane of rotation of mass 16 and perpendicularwith a protruding member 49 rigidly fixed to mass 16 radially therewith.Nozzles 54, 55 are equally spaced from member 49 at the null position ofmass 16. Fluid passages 23 and 24 which are connected to the input offluidic circuit 26 (not shown) are connected to passages 50 and 51,respectively, intermediate the fluid flow restrictor 53 and nozzle endsthereof. The operation of the acceleration sensor in FIGURE 45 may bebriefly described as follows: Under conditions of zero angularacceleration, nozzles 54 and 55 are equally spaced from member 49 andthus the back pressure developed in passages 23 and 24 due to the effectof the fluid jets impinging upon member 49 in the presence of fluid flowrestrictors 53 is equal in each of passages 23 and 24 such that thedifferential signal therebetween is zero. Under conditions of an angularmotion acceleration, mass 16 undergoes a rotational motion about itsaxis proportional to the magnitude of the external acceleration in theplane of mass 16, resulting in spring members 40 and 41 developing aflexure torque in the same direction as the external angular motionacceleration event 19 but in an opposing direction relative to the nullpoint. The rotational motion of mass 16 causes member 49 to more closelyapproach one of the nozzles 54 and 55. Thus, assuming that the externalangular motion accleration event 19 is in a clockwise direction, therotational motion of mass 16 is counterclockwise relative to the frame18 thereby developing a larger magnitude 2 back pressure in passage 23and a correspondingly smaller back pressure in passage 24. Thisdifference in back pressures is the differentially pressurized fluidsignal applied to fluidic circuit 26 and results in filtered, amplifiedoutput signal AP, at the output of circuit 26 as in FIG. 4a.

From the foregoing description, it can be appreciated that our inventionmakes available a new open-loop fluidic analog accelerometer which isfriction-free in operation, and is constructed of parts not requiringhigh precision such that the full advantage of the highly reliable fluidamplifiers used in our apparatus and in circuits connected to the outputthereof, may be utilized. Our accelerometer may be of the one-axis ortwo-axis .linear motion accelerometer ty e or angular motionaccelerometer type each providing an analog-type fluid output signal.The acceleration-sensitive portion of our accelerometer being comprisedof a flexure-mounted inertial mass responsive to the accleration eventis of relatively simple construction and provides a highly reliabledevice.

Having described several embodiments of our openloop fluidic analogaccelerometer, it is believed obvious that modification and variation ofour invention is possible in the light of the above teachings. Thus,addi tional or other fluid amplifier circuitry may be utilized influidic circuits 26, 27 as desired. Our accelerometer may also beutilized as a vibration sensor wherein frame 18 is rigidly attached to astructure undergoing vibration. When used as a vibration sensor, afiltered output of the center vent 25 is the output signal. It can beseen in FIG. 2 that, as vibration amplitude increases, this filteredoutput decreases proportionally over the output range of the vibrationsensor. This principle can be applied to the sensing of single or doubleaxis linear vibrations or to torsional vibrations using theaforementioned configurations. Obviously, the design parameters such asdamping ratio and specific dimensions may be different for our apparatuswhen used as a vibrator sensor but the physical appearance could be thesame, and functionally would be identical except for the fact that thecenter vent is now monitored. This vibration sensor is also consideredto be Within the scope of our invention. Finally, it should be obviousthat various shapes of the spring members and inertial masses other thanthat illustrated may also be employed and that such elements may beconstructed from a variety of materials dictated by the environment. Itis, therefore, to be understood that changes may be made in theparticular embodiments of our invention as described which are withinthe full intended scope of the invention as defined by the followingclaims.

What We claim as new and desire to secure by Letters Patent of theUnited States is:

1. An open-loop fluidic analog-type accelerometer comprising inertialmass means for sensing a selected external acceleratiofi'event andgenerating an analog-type pressurized fluid signal proportional to themagnitude of the sensed acceleration event wherein an inertial massportion of said means remains in a predetermined null position in theabsence of the acceleration event and is movable therefrom in thepresence of such acceleration event, and spring means for supporting theinertial mass portion,

the force resulting from said mass portion accelerating in response tothe external acceleration event causing flexure of said spring means andmotion of the inertial mass portion relative to the null position in adirection opposing the external acceleration event, the steady-statedisplacement of said inertial mass portion from the null position beingproportional to the magnitude of a constant magnitude externalacceleration event, and further comprising fluid receiver means alignedwith the predetermined null position of said inertial mass portion formonitoring the analog-type pressurized fluid signal in the region of thepredetermined null position wherein the average magnitude of themonitored signal decreases proportionally with increased amplitude of'vibration of said inertial mass portion.

9 10 2. The fluidic sensor set forth in claim 1 and further center ofthe receiver in the nonflexed state of said comprising spring member andis moved relative to the center means for filtering the monitored signalto thereby obposition during the vibration event for generating an taina pressurized fluid output signal having a maganalog-type pressurizedfluid signal having an avernitude varying inversely with the vibrationampli- 5 age magnitude varying inversely with the vibration tude.amplitude. 3. A fluidic analog-type vibration sensor comprising 4. Thefluidic vibration sensor set forth in claim 3 and inertial mass meanscomprising a body movable along further comprising at least one selectedaxis along which a vibration means for filtering the pressurized fluidsignal generated event is to be sensed and in response thereto, at theoutput of said receiver to thereby obtain a spring means comprising aresiliently flexible member pressurized fluid output signal having amagnitude for supporting the inertial body, said spring member varyinginversely with the vibration amplitude. having a first end thereofrigidly supported in position about which the spring member flexureoccurs References Cited and a second end providing rigid attachment forthe UNITED STATES PATENTS vibration-sensitive inertial body, said springmember provided with a fluid passage therethrough, g i et means forsupplying pressurized fluid to a first end of 3023626 3/1962 Her onnell336-30 XR said fluid passage, the second end of said fluid passageadapted for emission of a fluid jet therefrom 3153346 10/1964 Qmr'mbach73 516 XR and 3,224,279 12/1965 Galh et a1. 73-517 means rigidly fixedto a device undergoing the vibration 320L999 8/1965 Byrd 73*515 eventand comprising a first portion for providing F R I N PATENTS the rigidsupport for said spring member about which 69 329 1 1939 Germany.

the flexure occurs, and a second portion having a fluid receiveroriented downstream of the second end JAMES J. GILL, Primary Examiner ofsaid fluid passage and at the null position of said inertial bodywhereby the fluid jet issuing from the US. Cl. X.R. second end of saidfluid passage is directed into the 73- 15

